Because the dumbbell biceps curl is a relatively simple exercise -- with the palm facing forward, curl the dumbbell from your thigh to your shoulder -- few options exist for improving or changing the movement. Supination, a rotation of the forearm, while not appropriate to add to every set of arm curls, elicits different muscle activity than the standard dumbbell biceps curl.

Biceps Anatomy

Two muscle heads constitute the biceps brachii muscle, located on the front of the upper arm. The long head lies on the outer portion of the upper arm and the short head lies on the inner portion of the upper arm. Both muscle heads originate at the scapulae, or shoulder blade, extend down the upper arm, cross the elbow and attach to the forearm.

Biceps Brachii Movements

The primary responsibility of the biceps brachii muscle is flexing, or bending, the elbow joint, which is the only joint movement that occurs during an arm curl exercise. The upper arm remains locked by the side as you curl the weight up toward the shoulder. Do not rest the weight against the shoulder, as this removes tension from the biceps muscles. The biceps are involved in another arm movement: forearm supination, or exteriorly rotating the forearm so the palm faces up.

Supinated Dumbbell Curl

Adding supination to the standard dumbbell curl exercise works the biceps more completely than performing the exercise without supination. Hold a dumbbell in each hand, your arms relaxed at your sides and your palms facing in toward each other. Curl the weight up, rotating the forearms so your palms face the ceiling at the top of the movement. As you lower the weight, reverse the rotation so your palms face each other at the bottom of the movement.

Considerations

According to a study published in "Experimental Neurology," flexing the biceps activates muscle fibers on the lateral portion of the biceps long head and supinating the forearm activates muscle fibers on the medial portion of the biceps long head. Performing flexion and supination simultaneously also targets fibers predominantly on the medial portion of the muscle head. In order to effectively target all fibers of the biceps brachii muscles, do not add supination to every set of dumbbell biceps curls. Perform two to three sets without supination and two to three sets with supination.

About the Author

Based in Austin, Texas, Jolie Johnson has been in the fitness industry for over 12 years and has been writing fitness-related articles since 2008 for various websites. She received her Bachelor of Arts in English and philosophy from the University of Illinois.